1. Field of the Invention
The present invention relates to a video signal reproducing apparatus in an image fast locking system which feeds an external reference time code to the apparatus capable of reproducing video signals recorded on a magnetic tape and outputs the selected video signal coincident with such reference time code.
2. Description of the Prior Art
In any broadcasting station or editing factory, there is used a magnetic recording/reproducing apparatus such as a video tape recorder (hereinafter referred to as a VTR) which is capable of reproducing a designated video signal at a timing coincident with a reference signal supplied from an external unit.
Particularly in an editing mode, there is used, as such external reference signal, a time code representing the time and the frame number of a relevant image on a magnetic tape where one program has already been recorded, and the recorded program is rearranged in response to such time code. With regard to any commercial broadcast, its start time is determined in accordance with the time code generated in the broadcasting station.
Such time code is so standardized as to be readable by any of the various video apparatus. In the case of a magnetic tape with video signals recorded thereon, digital signals representing at least the hour, minute, second and frame number are recorded in a time code track formed in the longitudinal direction of the magnetic tape. Such digital signals are recorded also in a video track so as to be readable even when the magnetic tape is brought to a halt or is driven in a super-slow reproduction mode.
Generally a vertical interval time code (VITC) in the video track is recorded in a designated horizontal line during the vertical blanking interval, so that the halt position of the magnetic tape can be confirmed by reading out such signal even when the VTR is in a still reproduction state.
In the VTR capable of reading out the designated time code (VITC) and reproducing the desired image corresponding to such time code, when the time code TC(D) of the image to be reproduced is designated as shown in FIG. 3 for example, first the magnetic tape is driven in a normal-speed forward mode FW or reverse mode REV to the vicinity of the start position represented by such time code, and after overrunning the position of the time code TC(P) relative to a preroll point, the tape is driven in the reverse direction at 1/20 speed. And upon a reading of the time code TC(P) relative to the preroll point, the tape is brought to a halt at such point and then is placed in a standby state.
Subsequently, when a start signal is inputted at an instant t.sub.0, the tape is driven in a reproducing mode from the preroll point. However, the time code of the video data reproduced by the VTR immediately after the start fails to be completely coincident with the external reference time code, so that a phase modifier incorporated in the VTR or editing apparatus functions for lock-in at an instant t.sub.1 where the time code of the reproduced image coincides with the external reference time code.
Thus, in reproduction of the video data from a predetermined position by the VTR, it is impossible to obtain the desired reproduced data coincident with the external time code at least during the time from the start of the VTR operation to the termination of the phase modification, i.e. during the time (T) required until a coincidence is attained between the frame number designated by the external reference time code and the frame number of the reproduced image from the VTR.
Therefore, if the phase modification time (T) becomes as long as 5 seconds or so, some problems arise to exert various harmful influences on the editing or broadcasting work.
Meanwhile, for shortening the phase modification time (T), it is necessary to employ a large-sized motor in the tape drive mechanism and also an enhanced servo-mechanism to diminish the response time, hence inducing higher production cost of the VTR.